Update copy based on TW feedback

Issue: Workspaces Cluster Agents Admin Settings UI (#545241 - closed)

What does this MR do and why?

Updates the copy based on feedback from Technical Writing. As a result of this, the mtuation error handling logic was simplified to provide a generic error and log the more specific error message from the GQL response in the console.

References

• Issue: #545241 (closed)
• Copy feedback thread: #545241 (comment 2548244785)

Screenshots or screen recordings

Screenshot	Notes
empty_state.mov	The setting title and description as well as the empty state texts are updated based on feedback. Link in the setting description direct to the GitLab agent configuration documentation.
	(No change) error message on organization workspaces agents query error.
	Previously, the mutation error message fails to account for the multiple errors that we could expect from the backend. Now, the error message is made more general, with the specific error returned from the GQL response logged in the browser console.
	Popover text is also updated

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